In order for polymer electrolyte membrane fuel cells to be economical, the polymer electrolyte membranes need to operate for thousands of hours above 100 °C. While Nafion, by itself, does not perform well at higher temperatures, nanocomposites with silica suffer less at these temperatures from dehydration and are more mechanically robust. In this paper we study nanocomposites prepared by mixing monodisperse silica nanoparticles (eg. 30, 70, 130 nm in diameter) with Nafion in ethanol, then casting the mixtures and drying to afford membranes. We were initially interested how the size of the particles effected the proton conductivity, but we discovered that homogeneous mixtures were more difficult to form, especially with the larger particles. We used atomic force microscopy and scanning electron microscopy to characterize both sides of the films. We discovered that larger particles (>100 nm in diameter) would often phase segregate and float to the top of the cast solution. Smaller particles were more likely to be homogeneous, but we found that using more viscous solutions proved adequate in insuring homogeneous distribution of silica particles. Details of the study including conductivity measurements will be described.